Perhaps it's a question many people have asked, but how do I do to implement capability?

I now want my item to have a simple 27-slot inventory.

1. What else do I need to add a slot to the item stack through capability, besides a simple class of slot data (ItemStackHandler? In this case?), Item # initCapabilities?

1. When and for what is the method called Item # initCapabilities called? What should I return?

2. What is CapabilityItemHander.ITEM_HANDLER_CAPABILITY?

3. What does @CapabilityInject (IItemHandler) mean?

5 minutes ago, Zemelua said:

Perhaps it's a question many people have asked, but how do I do to implement capability?

This is a really detailed tutorial on how to use capabilities.

15 minutes ago, Zemelua said:

1. What else do I need to add a slot to the item stack through capability, besides a simple class of slot data (ItemStackHandler? In this case?), Item # initCapabilities?

If you just want a simple inventory attached to your item, you don't need much else besides an implementation of ICapabilityProvider that you return a new instance of in initCapabilities(). Of course you might also want a container and screen to interact with the inventory.

24 minutes ago, Zemelua said:

1. When and for what is the method called Item # initCapabilities called? What should I return?

initCapabilities() is called when a new item stack is created, and should return a new instance of an ICapabilityProvider that can be used to get the item stack handler for you item.

 

26 minutes ago, Zemelua said:

2. What is CapabilityItemHander.ITEM_HANDLER_CAPABILITY?

This is the capability for item handlers. You can use it to retrieve an item handler like this: someItemStack.getCapability(CapabilityItemHandler.ITEM_HANDLER_CAPABILITY)

 

29 minutes ago, Zemelua said:

3. What does @CapabilityInject (IItemHandler) mean?

The @CapabilityInject annotation injects a capability into a field, similar to how @ObjectHolder injects registry entries into fields. You shouldn't need to use it since you can just use CapabilityItemHander.ITEM_HANDLER_CAPABILITY to retrieve your capability.

// Test
	@Override
	public ActionResultType onItemUse(ItemUseContext context) {
		IItemHandler inventory = context.getItem().getCapability(CapabilityItemHandler.ITEM_HANDLER_CAPABILITY).orElse(new ItemStackHandler(27));

		if (!context.getWorld().isRemote()) {
			// add 3 diamonds to inventory slot 0, how?
			int test = // get inventory slot 0 itemstack
			context.getPlayer().sendMessage(new StringTextComponent(String.valueOf(test)), null);
		}

		return super.onItemUse(context);
	}

Thank you very much. It seems that I was able to implement capability, but I don't know how to manipulate the value (contents of the inventory) ......

29 minutes ago, Zemelua said:

but I don't know how to manipulate the value (contents of the inventory)

Check out the javadoc in IItemHandler, it is really detailed and should give you an idea of what methods to use to manipulate the inventory.

Thank you, now it works perfectly!